Type 135 (35 mm) photographic film unit is in the form of a cartridge or patrone having a filmstrip joined at one end to a spool held in a canister. The cartridge is commonly marketed in nominal 24 and 36 film frame exposure sizes, with the filmstrip rolled up within the canister except for a protruding leading portion of the filmstrip. One-time-use cameras are commonly marketed, which include a 35 mm film cartridge. In these cameras, the filmstrip is prewound out of the canister of the cartridge, into a coil in a film chamber of the camera. This prewinding can be provided in a dark environment and the film cartridge can be protected from light prior to loading. In that case, the leading portion of the filmstrip is available for image capture. As many as 27 film frames can be captured on a nominal 24 exposure cartridge and as many as 39 film frames can be captured on a nominal 36 exposure cartridge. (It is common practice in one-time-use camera manufacture to use a first film frame or a partial film frame for camera testing and/or preexposure of a stock image. This leaves 26 film frames on a nominal 24 exposure cartridge and 38 film frames on a nominal 36 exposure cartridge.)
During prewinding, withdrawal of the last film frame (number 27 for a 24 exposure film unit or 39 for a 36 exposure film unit) from the canister requires more force than is required for prewinding the rest of the filmstrip. This is due the fact that the last film frame adjoins a splice that must be pulled through the throat of the canister. The throat is lined with plush and tightly fits against the filmstrip to provide light-tightness. The splice is a segment of tape adhered to the end of the filmstrip. The other end of the tape is adhered or otherwise fastened to the spool.
Some types of one-time-use cameras, which have been prewound to withdraw the splice from the 35 mm film canister, exhibit a higher degree of film debris contamination than similar cameras in which prewinding is stopped prior to splice withdrawal. The film debris is small pieces of filmstrip emulsion layers. Other types of one-time-use cameras, do not exhibit this problem. In the latter cameras, filmstrips have complexly shaped perforations with rolled transverse edges. Each transverse edge is shaped like an undercut embankment, in that a portion of the edge is curled over and protrudes into the perforation opening. These complexly shaped perforations cannot be produced by single pass perforating techniques and equipment, in which a perforation is punched by a single, continuous movement of a punch through the filmstrip. Examples of single pass perforating techniques and equipment are disclosed in U.S. Pat. Nos. 3,656,384; 3,753,521; 4,854,203; 5,337,642; and 5,461,450. Single pass perforating produces edges having an initial flat shear surface extending to a tear surface that angles back away from the perforation opening.
U.S. Pat. No. 6,283,645 discloses a one-time-use camera having a film debris catching comb mounted in the camera to block debris from leaving the film canister chamber during prewinding. This approach has the shortcoming the film debris remains in the camera and, thus, presents a risk of recontamination. The dimensions given for the comb are also quite precise.
Conventional 35 mm film 200 has perforations 202 that are substantially rectangular (rectangular with rounded corners) in shape as shown in FIGS. 6 and 11. Teeth of film transport mechanisms have engagement portions that, in cross-section where the filmstrip is engaged, are also substantially rectangular.
It would thus be desirable to provide cameras, methods, and filmstrips, which reduce debris while allowing use of last, splice-adjoining film frames and single pass perforating.